[PATCH v4] mm/vmalloc: lock contention optimization under multi-threading

rulinhuang
2024-02-22T12:04:37Z

When allocating a new memory area where the mapping address range is
known, it is observed that the vmap_area lock is acquired twice.
The first acquisition occurs in the alloc_vmap_area() function when
inserting the vm area into the vm mapping red-black tree. The second
acquisition occurs in the setup_vmalloc_vm() function when updating the
properties of the vm, such as flags and address, etc.
Combine these two operations together in alloc_vmap_area(), which
improves scalability when the vmap_area lock is contended. By doing so,
the need to acquire the lock twice can also be eliminated.
With the above change, tested on intel icelake platform(160 vcpu, kernel
v6.7), a 6% performance improvement and a 7% reduction in overall
spinlock hotspot are gained on
stress-ng/pthread(https://github.com/ColinIanKing/stress-ng), which is
the stress test of thread creations.

Reviewed-by: Chen Tim C <tim.c.chen@intel.com>
Reviewed-by: King Colin <colin.king@intel.com>
Signed-off-by: rulinhuang <rulin.huang@intel.com>
---
V1 -> V2: Avoided the partial initialization issue of vm and
separated insert_vmap_area() from alloc_vmap_area()
V2 -> V3: Rebased on 6.8-rc5
V3 -> V4: Rebased on mm-unstable branch
---
mm/vmalloc.c | 43 +++++++++++++++++++++++--------------------
1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 25a8df497255..ce126e7bc3d8 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1851,7 +1851,6 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
int node, gfp_t gfp_mask,
unsigned long va_flags)
{
- struct vmap_node *vn;
struct vmap_area *va;
unsigned long freed;
unsigned long addr;
@@ -1912,19 +1911,18 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
va->vm = NULL;
va->flags = (va_flags | vn_id);

- vn = addr_to_node(va->va_start);
-
- spin_lock(&vn->busy.lock);
- insert_vmap_area(va, &vn->busy.root, &vn->busy.head);
- spin_unlock(&vn->busy.lock);
-
BUG_ON(!IS_ALIGNED(va->va_start, align));
BUG_ON(va->va_start < vstart);
BUG_ON(va->va_end > vend);

ret = kasan_populate_vmalloc(addr, size);
if (ret) {
- free_vmap_area(va);
+ /*
+ * Insert/Merge it back to the free tree/list.
+ */
+ spin_lock(&free_vmap_area_lock);
+ merge_or_add_vmap_area_augment(va, &free_vmap_area_root, &free_vmap_area_list);
+ spin_unlock(&free_vmap_area_lock);
return ERR_PTR(ret);
}

@@ -1953,6 +1951,15 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
return ERR_PTR(-EBUSY);
}

+static inline void insert_vmap_area_locked(struct vmap_area *va)
+{
+ struct vmap_node *vn = addr_to_node(va->va_start);
+
+ spin_lock(&vn->busy.lock);
+ insert_vmap_area(va, &vn->busy.root, &vn->busy.head);
+ spin_unlock(&vn->busy.lock);
+}
+
int register_vmap_purge_notifier(struct notifier_block *nb)
{
return blocking_notifier_chain_register(&vmap_notify_list, nb);
@@ -2492,6 +2499,8 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
return ERR_CAST(va);
}

+ insert_vmap_area_locked(va);
+
vaddr = vmap_block_vaddr(va->va_start, 0);
spin_lock_init(&vb->lock);
vb->va = va;
@@ -2847,6 +2856,8 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node)
if (IS_ERR(va))
return NULL;

+ insert_vmap_area_locked(va);
+
addr = va->va_start;
mem = (void *)addr;
}
@@ -2946,7 +2957,7 @@ void __init vm_area_register_early(struct vm_struct *vm, size_t align)
kasan_populate_early_vm_area_shadow(vm->addr, vm->size);
}

-static inline void setup_vmalloc_vm_locked(struct vm_struct *vm,
+static inline void setup_vmalloc_vm(struct vm_struct *vm,
struct vmap_area *va, unsigned long flags, const void *caller)
{
vm->flags = flags;
@@ -2956,16 +2967,6 @@ static inline void setup_vmalloc_vm_locked(struct vm_struct *vm,
va->vm = vm;
}

-static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
- unsigned long flags, const void *caller)
-{
- struct vmap_node *vn = addr_to_node(va->va_start);
-
- spin_lock(&vn->busy.lock);
- setup_vmalloc_vm_locked(vm, va, flags, caller);
- spin_unlock(&vn->busy.lock);
-}
-
static void clear_vm_uninitialized_flag(struct vm_struct *vm)
{
/*
@@ -3010,6 +3011,8 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,

setup_vmalloc_vm(area, va, flags, caller);

+ insert_vmap_area_locked(va);
+
/*
* Mark pages for non-VM_ALLOC mappings as accessible. Do it now as a
* best-effort approach, as they can be mapped outside of vmalloc code.
@@ -4584,7 +4587,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,

spin_lock(&vn->busy.lock);
insert_vmap_area(vas[area], &vn->busy.root, &vn->busy.head);
- setup_vmalloc_vm_locked(vms[area], vas[area], VM_ALLOC,
+ setup_vmalloc_vm(vms[area], vas[area], VM_ALLOC,
pcpu_get_vm_areas);
spin_unlock(&vn->busy.lock);
}

base-commit: 9d193b36872d153e02e80c26203de4ee15127b58
--
2.39.3